1. Field of the Invention
The invention relates to an electrical connector for use in providing power and data communications to electrical devices disposed in a wellbore.
2. Background Art
The completion phase of a well drilled through a petroleum reservoir normally starts with setting a production casing or liner in the well, and pumping completion fluid or drilling fluid into the well to contain pressure in the reservoir until the well is completed and ready to be produced. The well is completed by installing a production tubing string in the well and carrying out certain procedures which will allow fluids to be produced from the reservoir and carried to the earth""s surface through the tubing string. The term xe2x80x9ccompletion,xe2x80x9d as used herein, is an arrangement of mechanical elements within the well which allows fluid to be produced from or injected into the reservoir. The configuration of the completion depends on reservoir depth, fluid type, and pressure. In general, the completion includes the production tubing string for transporting fluids from the reservoir or production zone to the surface and a packer for isolating an annular space between the casing and tubing string. The production tubing string is suspended within the production casing by a wellhead assembly. A valve system is normally mounted on the wellhead assembly. The valve system includes an assembly of valves and fittings used to control production, contain reservoir pressure, and provide access to the production tubing string. The completion may also include a sand control device, e.g., screen and/or gravel pack, which filters sand from the produced reservoir fluid.
Regardless of how the well is completed, it is desirable and important to monitor reservoir parameters while producing fluids from the reservoir. Reservoir parameters such as pressure, temperature, fluid flow rate, and other parameters which provide useful information about the development and behavior of the reservoir may be monitored. Monitoring reservoir parameters requires that one or more sensors which are responsive to the reservoir and/or fluid flow parameters to be measured are suitably positioned in the well, and communication between the sensors and the reservoir is established. The information gathered from analysis of the measured parameters may then be used to control and optimize production as well as to predict changes that may occur in the reservoir over a time period.
Typically, when it is desired to monitor a reservoir, one or more sensors are attached to one end of an electrical cable (xe2x80x9cwirelinexe2x80x9d) or coiled tubing, and the wireline or tubing is inserted into the well. Communication between the sensor and the reservoir is then established. The sensor takes measurements and transmits the measurements to the surface or to a data recorder that is coupled to the sensor. After measurements are taken, the sensor is retrieved from the well and the measured data are analyzed. Certain well-control functions may be performed depending on the results of the analysis.
An alternative approach to monitoring reservoir parameters contemplates a system which integrates reservoir-parameter monitoring and well-control functions within the completion system itself. Such xe2x80x9cintelligentxe2x80x9d completion systems include a downhole system and a surface system. The downhole system is made of various modules which are capable of monitoring and controlling flow of fluids from one or more production zones into the production tubing string. The surface system interfaces with the downhole system to determine the position, status, and/or flow characteristics in each production zone. The surface system may send a command to the downhole system to actuate certain subsurface devices to alter certain flow parameters. The downhole system may also automatically control flow in the well.
Intelligent completion systems require reliable power and data communications to the downhole system, particularly during production. One method for providing power and data communications to the downhole system is to run an electrical cable from the surface to the downhole system. The electrical cable typically consists of two main sections. One main section is coupled to the downhole system and the other main section is coupled to a control module at the earth""s surface. To establish power and data communications between the downhole system and the control module, the two sections of the electrical cable must be connected. Typically, the connection is made at the wellhead, but it may also be made inside the wellbore itself. Making a connection inside the wellbore requires a xe2x80x9cwet-mateablexe2x80x9d electrical connector. In subsea completions, for example, the wellhead assembly and valve system are installed separately. Thus, a wet-mateable electrical connector is also required to make a connection at the wellhead. The electrical connection should be reliable to ensure reliable monitoring of reservoir parameters. For subsea completions, in particular, the electrical connection should be durable because the wellhead assembly and valve system are permanently installed on the sea floor. Also, the electrical connection should be able to insulate high voltage after being pressure sealed from conductive seawater and/or production fluid. This high voltage is often required for operation of downhole equipment and sensors.
The primary challenge in making wet electrical connections is how to protect the electrical contacts from influx of seawater and/or production fluid. This challenge has been addressed in a number of different ways. For example, U.S. Pat. No. 4,795,359 issued to Alcock et al. discloses an underwater electrical connector assembly having a male connector with a contact pin and a female connector with three closed chambers. The three closed chambers contain electrically insulating media, such as oil or grease. An electrically insulating shuttle piston extends through aligned holes in the three closed chambers and through a contact socket in one of the chambers. The shuttle piston is urged back when the contact pin of the male connector is engaged by the contact socket. An o-ring provides a seal between the holes in the chambers and the shuttle pin. The electrically insulating media provides a protected area around the connection between the contact pin and the contact socket. The chambers are made of a flexible membrane to permit variation of the pressure of the electrically insulating media inside them relative to the pressure outside the connector to reduce the tendency for water from the outside to enter the chambers.
U.S. Pat. No. 4,174,875 issued to Wilson et al., discloses a coaxial wet-mateable connector assembly wherein both the male and female connectors have concentric conductors. A rigid core dielectric material is disposed between the inner and outer male conductors for providing electrical insulation and a water-tight seal between them. An interconnection space is defined between the inner and outer female conductors. The female connector includes a spring-biased shuttle piston which is disposed and movable within the interconnection space. The shuttle piston has a central conductor with electrical contacts on either side for engaging the male and female inner conductors upon mating. To provide a fluid-tight seal between the shuttle piston and the female outer conductor before mating, a bulkhead is disposed within the interconnection space, adjacent the female outer conductor termination end. The bulkhead also provides a fluid-tight seal between the male inner conductor and the female outer conductor after mating, thereby preventing water from entering the interconnecting space. An o-ring seal wipes the male inner conductor clean of water as the male inner conductor drives the shuttle piston within the female housing until electrical interconnection between the male and female connectors is completed. A pressure compensating bladder removes fluid trapped within the interconnection surface during mating and returns the fluid to the interconnection surface during decoupling, thereby preventing a hydraulic lock between the male and female connectors.
U.S. Pat. No. 5,772,457 issued to Cairns discloses a pressure-balanced adapter for connecting two electrical connectors. The adapter comprises a shell having an internal chamber and a plurality of ports. The internal chamber has vents to the external environment. A plurality of electrically-conductive socket assemblies are disposed within the internal chamber, each in alignment with a respective one of the ports. Each of the socket assemblies has a piston which is movable in the port between an extended position and a retracted position. Each socket assembly is pressure-compensated to the ambient external pressure by means of one or more resilient bladders filled with dielectric fluid. Each socket assembly has one or more socket assembly vents. Each socket assembly also has contacts for engagement with electrical connectors. When the piston is in the extended position, it seals the port to prevent exposure of the socket assembly to the external environment. A flexible bladder containing dielectric fluid is disposed in the internal chamber and arranged to enclose at least the portion of each socket assembly in which the socket assembly vents are located. The exterior of the bladder is in fluid communication with the external environment through the chamber vents so that the pressure inside the socket assemblies is equalized with the pressure of the external environment.
Several other wet-mate type submersible electrical connectors are known in the art. See, for example, U.S. Pat. No. 4,039,242, U.S. Pat. No. 5,645,442, and U.S. Pat. No. 4,192,569. In general, prior art wet-mate type submersible electrical connectors use some type of elastomer component for sealing around a sliding piston, and also for the bladder (or membrane or diaphragm) component. The main purpose of the elastomer seal and bladder arrangement is to prevent intrusion of seawater and/or wellbore fluid into the electrical contact area. During long-term exposure to high pressure and temperature, however, well fluids, and/or moisture penetrate these elastomer seals and bladders, even though they are pressure-compensated and oil-filled. This moisture can easily build to the point where electrical short circuits can develop, causing connector failure. With the introduction of intelligent completion systems and advances in real-time well monitoring techniques, long-term dependability of this type of electrical connector has become crucial to the success of intelligent well completions.
In one aspect, the invention relates to a wet-mateable electrical connector which comprises a female connector body having an internal central cavity and a female metal sealing surface at a forward end. A female contact housing is disposed within the internal central cavity. The female contact housing includes one or more female contacts. A sliding pin is movably disposed within the internal central cavity. The wet-mateable connector further comprises a male contact pin having a front end for engagement with a front end of the sliding pin. The male contact pin includes one or more male contacts, each of which engages with a respective one of the female contacts during mating so as to establish electrical connection. The male contact pin has a male metal sealing surface which engages with the female metal sealing surface to form a metal-to-metal seal, thereby enclosing the male-to-female electrical contact area. The wet-mateable electrical connector further comprises a spring which applies a required force to the female connector body to activate the metal-to-metal seal.
In some embodiments, the wet-mateable electrical connector further comprises a metal bellows for pressure compensation and balancing between the internal central cavity and the exterior of the wet-mateable electrical connector. In some embodiments, the female connector body includes multiple female contacts and the male contact pin includes multiple male contacts, wherein each of the male contacts engages with a respective one of the female contacts to establish an electrical connection. In some embodiments, the male contact pin with all the multiple contacts embedded in it is molded as a one-piece solid body. In some embodiments, the wet-mateable electrical connector further comprises a wiper seal mounted at the forward end of the female connector body, wherein the wiper seal is arranged to provide effective wiping of the male contact pin prior to the male contact engaging the female contact.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.